Mild traumatic brain injury (TBI) is a major public health problem in the United States. While it is well established that children with severe TBI are at high risk for new psychiatric disorder, studies of children with mild TBI are plagued with methodological problems resulting in conflicting findings and fueling controversy. There is not a single psychiatric study of pediatric mild TBI that is free of problems related to definition of mild TBI, control groups, outcome measurements, longitudinal design, selection bias, sample size, or assessment of injury and psychosocial risk factors. The overall goal of the proposed project is to study injury and psychosocial risk factors for the development of new psychiatric disorders in children with mild TBI. The proposed study will involve a 1-year, 4-assessment, prospective longitudinal study of consecutively treated injured children with mild TBI (n=220) and a control group of children with mild orthopedic injuries not involving the brain (n=110). Assessments will include validated structured interviews to identify psychiatric disorders, adaptive behavior skills, academic achievement, intellectual function, family psychiatric history, and family function. Lesion identification, lesion localization, lesion volumetrics, regional volumetrics, and measures of white matter integrity, will be defined using high-resolution structural magnetic resonance imaging (MRI). MRI analyses will include diffusion tensor imaging, susceptibility weighted imaging, T2-weighted imaging, and fluid attenuated inversion recovery imaging. The study will examine three major hypotheses: (1) New psychiatric disorders in children will occur at a significantly higher rate in children with mild TBI compared with orthopedic controls. (2) New-onset psychiatric disorders in children will be predicted by child variables (pre-injury child adaptive function, pre-injury academic and cognitive function, and pre-injury lifetime psychiatric disorders), and pre-injury family variables (socio- economic status, pre-injury family function and life-events, family psychiatric history) in children with mild TBI and orthopedic injury. (3) The occurrence of new-onset psychiatric disorders will be mediated by post-injury child coping strategies and post-injury family variables (functioning and stressors) in children with mild TBI and orthopedic injury. Additionally, injury variables (severity, presence of a brain lesion, extent of diffuse axonal injury) will mediate occurrence of new-onset psychiatric disorders in children with mild TBI and orthopedic injury. This study will foster more accurate prediction, earlier identification and improved treatment of children with psychiatric complications related to mild TBI.